The invention relates to an apparatus for activating and/or deactivating a security device, particularly an entry device for a motor vehicle, having a portable transmitter unit for wirelessly transmitting a coded information item which is received by a receiver apparatus and is compared with a prescribed coded information item, the receiver apparatus being capable of outputting an actuation signal to the security device if the two information items match and the transmitter unit and the receiver apparatus being capable of being advanced in terms of the current coded information item.
Known apparatuses for activating and/or deactivating a locking system in a motor vehicle have a portable transmitter which, on request, transmits a coded information item to a receiver device which is permanently installed in the motor vehicle. The receiver device compares the transmitted coded information item with a prescribed information item which is generated in it. If the two information items match, the locking system is actuated by the receiver device.
So that it is still possible to operate the security device when the battery in the transmitter fails, for example, the receiver device is connected to a lock cylinder which can be operated mechanically using a key, which likewise activates or deactivates the security device.
Since, normally, only the remote control is used to actuate the locking system, it is necessary to ensure that only quite specific transmitters are able to unlock or lock a central locking system. The transmission protocols are therefore provided with a fixed allocation comprising a fixed code and an alternating code.
To calculate the respective next alternating code values, the same algorithm is used in the transmitter and in the receiver. In this context, the receiver has a so-called capture range for unlocking and locking, said capture range always permitting a plurality of future coded information items as being valid. The alternating code is changed in the transmitter by request; in the receiver, on the other hand, it is equated to that of the transmitter when a valid information item is received. Hence, if a plurality of coded information items from the transmitter do not reach the receiver, a permissible coded information item may be outside the capture range of the receiver and may thus not be recognized by the receiver.
Particularly when radio remote controls are used, where coded information items are transported over long ranges using a radio signal, interference within the transmission link may impair or completely interrupt the receiver""s reception of the coded information item transmitted by the transmitter. Such interference can be produced deliberately in order to record the coded information items transmitted by the transmitter and use them to open the motor vehicle without authorization.
If a user operates the transmitter unit more than once, he may be led to believe that the security device is operating correctly, as a result of one of the tapped transmitter telegrams being transmitted to the receiver device by the tapping device in a tapping pause and triggering the expected reaction there, even though the transmitted message has not been transmitted by the authorized transmitter. The user therefore thinks that his vehicle is properly locked. In the meantime, unauthorized persons can use the other tapped transmitter messages, which are more recent than the telegram transmitted by the tapping device, to gain entry to the motor vehicle.
The invention is thus based on the object of providing an apparatus for activating and/or deactivating a security device in which unauthorized deactivation of the device is reliably prevented.
The invention achieves the object by the feature that the transmitter unit and the receiver apparatus are automatically advanced n times after a prescribed interval, the prescribed interval being only insubstantially longer than the delay time for the signal carrying the coded information item from the transmitter unit to the receiver apparatus at a maximum range for the receiver apparatus.
The abrupt advancement of the valid coded information item ensures that all tapped signals are safely in the past and are recognized by the receiver apparatus as being invalid. This means that just a short time after the tapping attempt described above the code sequences stored in the tapping unit are regarded by the receiver apparatus as being past alternating code sequences which can no longer be used to open the vehicle. In this context, the prescribed interval is set such that the operator is still close to the vehicle.
Advantageously, the prescribed interval is started in the receiver device after a valid information item has been received, and is started in the transmitter unit after the transmission of a coded information item has ended.
To prevent the capture range of the receiver apparatus from being exceeded by the coded information item in the portable transmitter unit after a particular time, the code generator in the portable transmitter unit and the code generator in the receiver apparatus are advanced by the same number of steps.
Advantageously, the receiver apparatus is connected to a mechanical device which can be operated using a key, the receiver apparatus being disabled for the reception and/or evaluation of the coded information item and/or for the output of the actuation signal to the security device after the security device has been mechanically activated, the block being lifted after the security device has been mechanically deactivated.
This has the advantage that if the user establishes, after operating the transmitter a plurality of times, that the receiver is not reacting to the transmitted transmitter signals and the desired action cannot be carried out, he can deactivate the security device in the conventional manner by inserting the key into the lock cylinder and unlocking or locking the security device. However, since the radio remote control is put out of operation at the same time as this mechanical locking, this also reliably prevents tapped coded information items which have not yet been registered by the receiver from being able to be used to deactivate the security device. Only after mechanical deactivation of the security device does the radio remote control work in the customary manner again.
A coded information item transmitted from the transmitter to the receiver directly after the security device has been mechanically deactivated is used to shift all coded information items, possibly recorded beforehand, to the realms of the past, since the receiver, having received a valid information item from the transmitter, equates said information item to the one which is present in the receiver. This means that they are outside the capture range of the receiver, so that no actions can be triggered using these tapped coded information items.
This takes place particularly quickly and reliably if the receiver apparatus, having established that the security device has been mechanically deactivated, sends a stimulus signal to the portable transmitter unit for transmission of the coded information item.
Advantageously, the portable transmitter unit and the receiver apparatus each contain a code generator, the first code generator in the portable transmitter unit generating the coded information item which is to be transmitted, and the second code generator in the receiver apparatus generating the prescribed coded information item, both code generators operating on the basis of the same algorithm.
In this context, one or more respective random numbers which are independent of one another may be used as code, said random numbers being processed and compared with one another in the receiver on the basis of particular arithmetic rules.